As AMp'D.2play mentioned, I hear a Maj6 arpeggio. Another way to think of it is major pentatonic, but without the 2nd. In a live setting, I think you could get away with dominant 7 as well (root, maj3rd, 5th, minor 7th, octave: A C# E G A). It does affect the quality of the song, but the crowd should be able to dance either way.
This is the kind of song that I don't mind playing, but for whatever reason the guitar players that have wanted to do it always want to hear the bassline from the record. I am not interested in being human juke box, so I will basically play "blues in A". It feels antithetical to me to have a highly orchestrated 3 chord blues song. I'll adjust the energy for the feel of the song, and do my best to make it groove.
Pedulla Club #136, VM Jaguar Club